The present invention relates to testing of semiconductor light emitting devices, more particularly, the invention relates to a method and apparatus for collecting light from a linear array of edge emitting semiconductor laser or LED devices.
Semiconductor light emitting devices, e.g., edge emitting laser diodes or light emitting diodes (LED), are well known in the art. Such devices are manufactured on wafers which, after initial manufacture and processing (e.g. thinning down and trimming), are separated into a predetermined number (e.g., three) of smaller units, generally referred to as wafer sections. These sections are typically further trimmed in one dimension, generally referred to as length, to a predetermined size. Semiconductor laser or LED bars are produced from a semiconductor wafer section by a scribing and cleaving procedure, wherein predefined shapes of bars are delineated by scribing lines and the bars are separated by cleaving along the scribing lines. Accurate cleaving along the scribed lines is possible because of the brittle nature of the sections.
A typical semiconductor LED or laser bar includes a p-contact surface, generally referred to as the top surface, and an n-contact surface, generally referred to as the back surface. The p-contacts and n-contacts are produced by a fabrication sequence including a metallization process in which the surfaces of a semiconductor wafer are selectively coated with a metallic layer. Individual semiconductor laser or LED devices on the bars may be activated by applying an electric current across the n-contacts and p-contacts, respectively, of the devices. During processing, the bars are typically supported by a flexible, adhesive, holding surface. After processing, the bars may be removed from the holding surface for testing or the devices may be tested while the bars are attached to the holding surface.
Testing of edge emitting semiconductor lasers or LEDs involves measurement of the light intensity emitted by the laser or LED devices at a predefined wavelength spectrum, while applying a predetermined current using electrical probes, namely, a p-contact probe and an n-contact probe. To ensure accurate comparative testing of the laser or LED devices, the light emitted by the devices must be collected at a precise, reproducible manner, e.g., at a predefined distance or angle, and delivered to a light detector using appropriate optics. Typically, a plurality of laser or LED devices are included in each semiconductor bar. To test individual laser or LED devices along the bar, the light detector and associated optics, as well as the p-side electrical probe, must be separately aligned for each device being tested. For reliable comparative testing of the laser or LED devices, the p-contact alignment procedure requires complex and tedious positioning equipment and/or software to ensure consistency in collecting and detecting the light emitted by the laser or LED devices. The n-contact does not require realignment for each device being tested because the semiconductor bar includes a common n-contact for all the laser or LPD devices thereon.
The present inventors have developed a method and apparatus for testing light emission from a series of edge emitting semiconductor laser diodes or LEDs, using a light collection arrangement and a p-contact electrical probe, without requiring movement and/or realignment of the laser or LED bar, the light collection arrangement or the p-contact electrical probe.
In accordance with the present invention, the light emitted by individual laser or LED devices along a laser or LED bar is collected sequentially by a fixed funnel-shaped light guide (hereinafter referred to as: xe2x80x9clight funnelxe2x80x9d) which directs the light emitted by the individual laser or LED devices to a light detector. In accordance with an aspect of the present invention, a series of laser or LED bars, which may be mounted on a holding substrate, may be sequentially brought to a predefined position aligned with the light funnel. A selectively activated electrical probe arrangement, including a plurality of individually addressable p-contact probes, is brought into contact with the laser or LED bar, such that each p-contact probe is in contact with a respective p-contact. A switching device may be used to selectively apply biasing voltage to the to the individual laser or LED devices along the bar, via the respective p-contact probes, and the light emitted by each individual laser or LED device is collected by the fixed light funnel. Thus, once the laser or LED bar is appropriately positioned with respect to the light funnel, and the p-contact probe arrangement is brought into contact with the respective p-contacts of the bar, the relative physical positions of the bar, the flight funnel and the p-contact probe arrangement remain fixed during testing of all the laser or LED devices on the bar.
An embodiment of the present invention thus provides apparatus for sequentially testing the light emitted by a group of semiconductor light emitting devices, each device having a p-contact, arranged to emit light over a testing area. The apparatus includes a light detector and a light funnel which has a collection end, constructed to capture light over substantially the entire testing area, and a detection end. The detection collects light emitted by any of the light emitting devices and the detection end directs the collected light to the light detector. The apparatus further includes an electrical probe arrangement including a plurality of p-contact probes which are selectively connectable with the p-contacts of respective light emitting devices in the group of light emitting devices. The apparatus may further include a support device for securely positioning the group of semiconductor light emitting devices aligned with the collection end of the light funnel. Additionally, the apparatus may include a switching device for selectively supplying a predetermined electrical current, via the p-contact probes, to the p-contacts of selected ones of the light emitting devices.
The present invention also provided a method for sequentially testing the light emitted by a group of semiconductor light emitting devices, each light emitting device having a p-contact, arranged to emit light over a testing area. The method includes placing an electrical probe arrangement including a plurality of p-contact probes in contact with the p-contact of respective light emitting devices in the group of light emitting devices, selectively activating selected ones of the light emitting devices in the group of light emitting devices to emit light over the testing area, guiding the light emitted by the selectively activated light emitting devices via a light funnel which captures light substantially over the entire testing area, and detecting the light guided by the light funnel. In an embodiment of the present invention, the light emitting devices are selectively activated by selectively supplying an electrical current to the p-contacts of the selected light emitting devices via their respective p-contact probes. The group of semiconductor light emitting devices are preferably securely positioned at a fixed position with respect to the collection end of the light funnel.